For region to the north see:

USGS Open File Report 2010–1083-K

Middle East and vicinity

http://pubs.usgs.gov/ofr/2010/1083/k

I n d i a n O c e a n 

NTD

KR

DR

LM

LR

LT

LAKE

WNR

ER

Gulf of Aden

Red Sea

DJIBOUTI

Asmara Sanaa

Addis Ababa

Omdurman

Khartoum

Aden

Mogadishu

Kampala

Nairobi

Mombasa

Antananarivo

Beira

Blantyre

Fianarantsoa

Dar es Salaam

Kisangani

Kananga

Mbuji-Mayi

Lumumbashi

Ndola

Lusaka

Harare

Bulawayo

Ar Rub‘ al Khali

Desert

MAP EXPLANATION

Active volcanoes Rift zone

Plate boundaries

East African Rift System

 segment boundary and 

 identifier

Divergent

Inferred

Greater than 6.0 magnitude

earthquake location

5.0–5.5

5.5–6.0

Less than 4.5

4.5–5.0

Magnitude classes

Greater than 6.0

DR

1985

Interferogram of Magmatic Intrusions

SUDAN

YEMEN

SAUDI

ARABIA

CENTRAL AFRICAN

REPUBLIC

DEMOCRATIC REPUBLIC

OF THE CONGO

CHAD

ETHIOPIA

SOUTH SUDAN

UGANDA

KENYA

SOMALIA

TANZANIA

ZAMBIA

MOZAMBIQUE

MALAWI

ZIMBABWE

BOTSWANA SOUTH

AFRICA

ANGOLA

NAMIBIA

RWANDA

BURUNDI

DJIBOUTI

ERITREA

Omdurman Khartoum

Addis Ababa

Mogadishu

Nairobi

Kampala

Mombasa

Dar es Salaam

Lubumbashi

Lusaka

Harare

Sanaa

20°E 30°E 40°E 50°E

10°N

20°N

10°S

20°S

0°

1985

Lake

Albert

DATA SOURCES

Seismic Hazard

2006

Lake

Malawi

WGS 1984 Projection

Lake 

Tanganyika

1990

Cartography: Eric S. Jones

Cartography Database: Eric S. Jones, Gregory M. Smoczyk

Lake

Edward

1989 1978

Dobi graben

Swarm

Afar Triple Junction

Afar Triple Junction

RIFT ZONES

Lake 

Rukwa

In the East Africa Rift System, rifting and deformation is understood to be more broadly distributed than along

a single linear feature; as such, we represent the approximate width of the deformation zones here with gray

zones. The shaded regions here are meant to be representative of distributed deformation, rather than precisely

defining the extent of that deformation. In this interpretation, plate boundaries represent the rift axis.

Lake

Victoria

Lake

Turkana

The earthquake locations shown on the main map (left) and on the depth profiles are taken from the global

1900–2007 Centennial catalog (Engdahl and Villaseñor, 2002), a catalog of high-quality depth determinations

for the period 1964–2002 (Engdahl, personal comm., 2003), and USGS-NEIC for the period 2003-2013. Major

earthquakes (M>=6.0) are labelled with the year of occurrence (Tarr, and others, 2010).

The seismic Hazard and Relative Plate Motion panel displays the generalized seismic hazard of the region

(Giardini, and others, 1999) and representative relative plate motion vectors using the MORVEL model 

(DeMets, and others, 2010.).

Base map data sources include GEBCO (2008), Esri’s Ocean Basemap, Volcanoes of the World dataset (Siebert

and Simkin, 2002), plate boundaries (Bird, 2003), and Digital Chart of the World (1992).

1990

1928

Lake

Kivu

Seismicity of the Earth 1900–2013

East African Rift

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Compiled by Gavin P. Hayes,1 Eric S. Jones,1 Timothy J. Stadler,1 William D. Barnhart,1

Daniel E. McNamara,1 Harley M. Benz,1 Kevin P. Furlong,2 and Antonio Villaseñor3

2

Department of Geosciences, Pennsylvania State University, University Park, Pa., USA

1

U.S. Geological Survey

3

Institute of Earth Sciences, Consejo Superior de Investigaciones Científicas, (CSIC), Barcelona, Spain

2014

30°E

20°S 20°S

10°S 10°S

0° 0°

10°N

20°N

10°N

20°N

40°E

30°E 40°E

KILOMETERS

0 250 500 750 1,000

0 250 500 750 1,000

MILES

SCALE 1:8 500 000 

Open-File Report 2010–1083-P

SAUDI

ARABIA

ERITREA

SUDAN

CENTRAL

AFRICAN

REPUBLIC

SOUTH

SUDAN

ETHIOPIA

SOMALIA

UGANDA

KENYA

TANZANIA

MADAGASCAR

MOZAMBIQUE

MALAWI

SEYCHELLES

MAYOTTE

COMOROS

RWANDA

BURUNDI

DEMOCRATIC

REPUBLIC OF

THE CONGO

ANGOLA

ZAMBIA

BOTSWANA

ZIMBABWE

SOUTH

AFRICA

NAMIBIA

FRENCH SOUTHERN AND

ANTARCTIC LANDS

CHAD

YEMEN

MAP LOCATION

SUMMARY

The East African Rift system (EARS) is a 3,000-km-long Cenozoic age continental rift extending from the Afar 

triple junction, between the horn of Africa and the Middle East, to western Mozambique. Sectors of active extension 

occur from the Indian Ocean, west to Botswana and the Democratic Republic of the Congo (DRC). It is the only rift 

system in the world that is active on a continent-wide scale, providing geologists with a view of how continental 

rifts develop over time into oceanic spreading centers like the Mid-Atlantic Ridge.

Rifting in East Africa is not all coeval; volcanism and faulting have been ongoing phenomena on the continent since 

the Eocene (~45 Ma). The rifting began in northern East Africa, and led to the separation of the Nubia (Africa) and 

Arabia plates in the Red Sea and Gulf of Aden, and in the Lake Turkana area at the Kenya-Ethiopia border. A 

Paleogene mantle superplume beneath East Africa caused extension within the Nubia plate, as well as a first-order 

topographic high known as the African superswell which now includes most of the eastern and southern sectors of 

the Nubia plate. Widespread volcanism erupted onto much of the rising plateau in Ethiopia during the Eocene-Oligocene (45–29 Ma), with chains of volcanoes forming along the rift separating Africa and Arabia. Since the initiation of rifting in northeastern Africa, the system has propagated over 3,000 km to the south and southwest, and it 

experiences seismicity as a direct result of the extension and active magmatism.

Today extension and magmatism are localizing in distinct eastern, western, and southwestern branches marking the 

edges of two or more microplates between the sub-parallel zones of extension in East Africa. The borders of the 

microplates (known as Victoria and Rovuma) with the Nubia plate to the west and Somalia plate to the east now 

represent the most seismically active zones on the continent where normal faulting earthquakes occur on a monthly 

basis. They are also the sites of volcano-tectonic earthquakes. Along the rift, models of sparse Global Positioning 

System (GPS) data and earthquake-slip vectors predict average spreading rates of 1–4 mm/yr, increasing from north 

to south in the western branch, and increasing from south to north in the east. 

Seismicity in the East African Rift is widespread, but displays a distinct pattern. Seismicity is characterized by 

mainly shallow (<40 km) normal faults (earthquakes rupturing as a direct result of extension of the crust), and 

volcano-tectonic earthquakes. The majority of events occur in the 10–25-km depth range. This pattern is widespread 

throughout the EARS, and provides insight into the relationship between depth of earthquakes, the deformation of 

continental lithosphere, and magmatic processes in many sectors of the rift.

The three limbs of the Afar triple junction zone experience major earthquakes, as well as frequent volcanic eruptions 

and dike intrusions. The magnitude of earthquakes during volcano-tectonic events is usually less than magnitude 6 

(M6), but large volumes of magma accommodating plate opening may occur during these intense, smaller magnitude swarms. The largest earthquakes recorded in this area occurred in a swarm, along a section of the evolving 

Arabia-Nubia plate boundary in Afar in August 1989. Studies of this earthquake swarm show that the events 

occurred as a result of slip on conjugate normal faults bounding the narrow Dobi graben. The swarm, made up of 25 

M≥4.2 earthquakes, occurred over 48 hours from 11:17 UT August 20, 1989. The events were all shallower than 15 

km as a result of the thin crust beneath the triple junction compared to the surrounding continental crust. Conversely, the deepest earthquake ever recorded on the African continent (~62 km) also occurred beneath the Afar triple 

junction on November 8, 1978. This M4.9 earthquake occurred beneath an active spreading segment, and was 

probably associated with the movement of magma at depth during the rifting episode.

The western branch is divided into three main segments: The northern and middle segments border the Nubia-Victoria microplate boundary, and the southern segment borders the Nubia-Rovuma boundary. The northern segment 

comprises the West Nile region (WNR), and Lakes Albert, Kivu, and Edward (LAKE); the middle segment includes 

Lakes Tanganyika and Rukwa (LT, LR); and the southern segment encompasses Lake Malawi and central Mozambique (LM). The two largest instrumentally recorded events in Africa occurred about 300 km north of Lake Albert 

in the WNR, in an area of Mesozoic (250–65 Ma) rifting. These M7.1 earthquakes struck four days apart in May 

1990, both at ~15 km depth. Their tectonic relationship to the Albert rift system or Mesozoic faults remains unclear. 

The most recent major earthquake to strike the region occurred on February 22, 2006. This M7.0 event struck at a 

depth of 11 km in west-central Mozambique around midnight local time, killing two and injuring 15. The earthquake was felt in Mozambique, Zimbabwe, Swaziland, South Africa, and Zambia, but no major structural damage 

was reported.

The eastern branch is a discontinuous system of rifts, most of which have experienced magmatism since their onset. 

From north to south, these are the Ethiopian Rift (ER), the Kenya Rift (KR), the northern Tanzania divergence 

(NTD), and the Davie Ridge (DR). The Kenya Rift experienced a major M6.9 earthquake in 1928, but has hosted 

only small magnitude swarms since then. As in the Afar and Ethiopian rift sectors where magma supply appears to 

be abundant, dike intrusions in the Kenya Rift accommodate extensional strain at lower stress levels than are 

required to cause slip along large fault systems bounding the rift. This generally results in relatively smaller earthquakes. Seismicity near the northern Tanzania Divergence marks the diffuse, volcanically active Victoria-Somalia 

plate boundary. Consistent with the widespread magmatism in this rift sector, earthquake magnitudes are generally 

less than M6, and are the result of normal faulting. The Davie Ridge marks the Rovuma-Somalia plate boundary in 

the oceanic lithosphere of the western Indian Ocean basin. On May 14, 1985, two M6.0–6.3 earthquakes struck this 

area, less than 100 km off the coast of northern Mozambique.

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Figure 1. Most of the tectonic processes active in the East African Rift System are related to rifting and associated 

magmatic intrusions. These processes are generally accompanied by significant crustal deformation, which can be 

imaged directly through the use of Interferometric Synthetic Aperture Radar (InSAR). InSAR is a remote sensing 

technique that uses two or more synthetic aperture radar images collected before and after a deformational event to 

generate maps of the surface displacements associated with that process, by exploiting differences in the phase of the 

waves returning to the satellite. This figure shows an example of the phase changes and associated deformation 

caused by a dike intrusion in October 2008, in Ethiopia generated from data collected by the Advanced Land Observing Satellite (ALOS) on September 19, 2008, and December 15, 2008. The ‘fringes’ in the resulting interferogram 

(each color cycle from blue to blue) represent approximately 12 cm of deformation in the radar’s line of sight. This 

interferogram shows displacements caused by surface spreading and subsidence due to the shallow injection of 

magma, and the formation of dikes rising from a deeper magma source. The complex signal near the center of the 

fringes also indicates surface cracking and faulting that occurs as the injected magma approaches and breaches the 

Earth’s surface. We have overlaid the interferogram on a three-dimensional schematic (and generic) interpretation of 

the magmatic intrusion event that caused this pattern of surface deformation.

AFRICAN

(NUBIA)

PLATE

Victoria

Microplate

Rovuma

Microplate

SOMALIA

PLATE

ARABIA

PLATE

FIGURE EXPLANATION

10% in 50 year peak ground

 acceleration

0–0.2 m/s2

0.2–0.4

0.4–0.8

0.8–1.6

1.6–3.2

3.2–6.4

6.4–9.8

Plate boundaries

Divergent

Other

500 750 1,000

KILOMETERS

0 250

500 750 1,000

MILES

0 250

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Suggested citation:

Hayes, G.P., Jones, E.S., Stadler, T.J., Barnhart, W.D., McNamara, D.E.,

Benz, H.M., Furlong, K.P., and Villaseñor, Antonio, 2014, Seismicity of

the Earth 1900–2013 East African Rift: U.S. Geological Survey 

Open-File Report 2010–1083-P, 1 sheet, scale 1:8,500,000

http://dx.doi.org/10.3133/of20101083P. 

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/of20101083P